1. Prior Art
In integrated circuit fabrication technology, read-only-memory (ROM) devices are implanted during processing with binary codes according to special or custom orders. However, it is difficult during the wafer processing to verify whether the code content in a ROM is correct or not, so that currently whether the intended or the real code id was actually implanted is not confirmed until after fabrication processing is completed when chip probing yield testing is performed on the wafer. The difficulty stems from, among other things, the fact that when wet dipping is used during processing after code implantation further oxide loss is caused and the process window becomes marginal, leaving insufficient time for testing. Also, in 0.6.mu. or less processing, implementation of the code dip is not suitable because it will result in process integration problems with oxide loss and implant dosage. Hence, presently in the art, defective ROMs are not tested and detected until after fabrication has been completed.
2. Problem to be Solved
Due to the inability to test the ROMs for correct coding during processing, erroneous coding may not be identified until after fabrication and shipping so that the cycle time for making adjustments to the process when errors are found to occur is extended beyond an optimum period. Also, ROMs with erroneous code content may pass through the testing.
3. Objects
It is therefore an object of the present invention to provide a method and means to save cycle time by identifying ROM code id during processing rather than waiting for subsequent yield testing after fabrication completion.
It is another object of the invention to guarantee a ROM code content 100% consistent with that ordered in a semiconductor wafer having a ROM array.